Intracellular and extracellular recordings will be made from single neurons within the myenteric plexus of the guinea-pig ileum. The tissue will be maintained in vitro and substances will be applied to the neurons by iontophoresis and by bath application in known concentrations. Neurons will be stained by intracellular injection of various dyes and a correlation will be sought between the function and electrophysiological proporties of the neuron, and its anatomical features. The actions of catecholamines and indolealkylamines on the neurons will be investigated. The actions of various peptides which normally exist within the neurons of the myenteric plexus will be studied on single neurons - these peptides include substance P, neurotensin, somatostatin enkephalin and vasoactive intestinal peptide. The results are expected to be of significance in the study of gastrointestinal motility, opioid pharmacology and to peptide neuroscience.